A blonde city girl named Amy marries a Colorado rancher. One morning, on his way out to check on the cows, the rancher says to Amy, "The insemination man is coming over to impregnate one of our cows, so I drove a nail into the 2x4 just above where the cow's stall is in the barn. Please show him where the cow is when he gets here, OK?"

The rancher leaves for the fields. After a while, the artificial insemination man arrives and knocks on the front door. “I came to inseminate the cow,” he said.

Amy takes him down to the barn. They walk along the row of cows, and when Amy sees the nail, she tells him, "This is the one right here."

The man, assuming he is dealing with an airhead blonde, asks, "Tell me, lady, 'cause I'm dying to know. How would YOU know that this is the right cow to be bred?"

"That's simple," she said. "By the nail that's over its stall," she explains very confidently.